• Insects have 3 body segments:
  Head contains the brain, mouth, eyes, antennae. Thorax is where 6 legs and possibly wings are attached.
  Abdomen holds digestive and reproductive organs.

• Arachnids such as mites and pseudoscorpions have 2 body segments:
  Cephalothorax is the fusion of head and thorax; 8 legs are attached here.
  Abdomen is similar to that of an insect.

• Decapods such as crayfish have 20 segments grouped into 2 parts:
  Cephalothorax is the fusion of head and thorax; 10 legs are attached here.
  Abdomen contains appendages called swimmerets used for swimming and brooding eggs.

Note the pseudoscorpion's pincer-like pedipalps should emerge from its mouth, and 8 legs should be attached to the cephalothorax.